1. Field of the Invention
The present invention relates to a sealing part and a substrate processing apparatus, and in particular relates to a sealing part used in a substrate processing apparatus that forms a plasma from a reactive active gas and processes a substrate using the plasma.
2. Description of the Related Art
A plasma processing apparatus that carries out plasma processing such as etching on semiconductor wafers as substrates has a vacuum chamber the pressure inside of which can be reduced down substantially to a vacuum. The etching is carried out on a semiconductor wafer housed in the vacuum chamber using a processing gas that is turned into a plasma in the vacuum chamber. In such a plasma processing apparatus, a ring-shaped sealing part is used to seal the inside of the vacuum chamber (the vacuum) from the outside (the atmosphere) (see, for example, U.S. Pat. No. 6,689,221). In particular, for an etching apparatus as the plasma processing apparatus, the semiconductor wafer becomes hot due to receiving energy from the plasma, and hence an O-ring made of a heat-resistant fluoro-rubber is used as the sealing part.
In recent years, etching in which a mixed gas containing a reactive active gas (e.g. a CxFy gas such as C4F8 gas) is used as the processing gas so that the etch rate is controlled by reaction by-products has become the mainstream. In such etching, when the reactive active gas is turned into the plasma, depositable active species such as fluorine radicals are produced.
Moreover, in etching using a reactive active gas, reaction by-products become attached to the inner wall of the vacuum chamber. The attached reaction by-products are stripped off to become particles, which become attached to semiconductor devices on the semiconductor wafer, bringing about a decrease in the semiconductor device yield. Dry cleaning is thus carried out to remove attached reaction by-products in the plasma processing apparatus. For example, WLDC (wafer-less dry cleaning), which is one type of dry cleaning, may be carried out. In the WLDC, the reaction by-products are removed by oxygen ions produced from oxygen gas. However, oxygen radicals are also produced at the same time.
The above fluoro-rubber is readily worn away by radicals (fluorine radicals and/or oxygen radicals). In a plasma processing apparatus in which a reactive active gas is used, a double sealing structure comprised of an O-ring-shaped sealing part (RTR (radical trap ring)) made of a radical-resistant fluororesin (specifically Teflon (registered trademark)) disposed on the vacuum side, and an O-ring made of a fluoro-rubber (specifically a vinylidene fluoride type rubber (FKM)) disposed on the atmosphere side is thus used. The RTR is comprised of a Teflon (registered trademark) tube, and rubber filled into the tube.
According to such a double sealing structure, the RTR seals in the radicals so that the radicals do not leak out from the vacuum side, and the fluoro-rubber O-ring seals the vacuum in the vacuum chamber from the outside atmosphere. For the double sealing structure, two sealing grooves for housing the RTR and the fluoro-rubber O-ring respectively are required, and hence a predetermined sealing space is required.
However, conventional plasma processing apparatuses have not been designed assuming the use of a double sealing structure, and hence the predetermined sealing space cannot be secured, and thus using a double sealing structure as described above in a conventional plasma processing apparatus is difficult. In particular, with a KF flange joint structure used for joining two pipes (JIS G 5526), providing two sealing grooves is structurally impossible, and hence a double sealing structure as described above cannot be used.
In the case that a double sealing structure cannot be used, an O-ring made of a radical-resistant fluoro-rubber (specifically a tetrafluoroethylene-perfluorovinyl ether rubber (FFKM)) is used, but FFKM is very expensive, and moreover has a poorer radical resistance than Teflon (registered trademark). In particular, in recent years, it has come to be strongly demanded for plasma processing apparatuses to have a long lifetime, and hence with FFKM a durability satisfying the requirements of plasma processing apparatus users cannot be secured.